There are many variables involved when striking a golf ball with a putter. Some of these variables are independent with respect to putter design, such as putting surface irregularities and individual putting techniques. However, the functional design of a putter can aid in the accuracy of striking a golf ball toward an intended target with desired linear and rotational velocities. Some previous putter designs have utilized unique balancing schemes of a putter head, and incorporated large moments of inertia or radii of gyration of the putter head about a specified point of rotation. It is generally known that the comfort and aesthetics of a putter are considered important to a golfer. Many putters have been designed with these functional and aesthetic qualities in mind. The above design features and other attributes of a putter can be classified as controllable variables. Many putters have addressed one or more controllable variables from a static and/or dynamic viewpoint in an attempt to improve the accuracy of a golfer's putting stroke. One such controllable variable is shaft location with respect to a putter head. Critical alignment of a shaft with one or more certain features of a putter head can improve the accuracy of a putting stroke.
For example, one prior putter, U.S. Pat. No. 5,131,656, describes a gravity balanced and faced balanced arrangement. When the centerline of the shaft extends through the center of gravity of the putter head the condition is defined as gravity balanced. A gravity balanced putter eliminates any torquing about the shaft axis caused by the force of gravity. When the putter face is horizontally upward, and the sum of the moments about the shaft centerline passing through the putter head are zero, the putter is defined as faced balanced. A faced balanced putter is claimed to produce zero torquing of the putter head about the shaft axis during the acceleration of the putter head through the impact zone. There are several disadvantages associated with the foregoing conditions. Firstly, the placement of the shaft must satisfy the two balanced conditions just described. This places strict limitations on the position of the shaft with respect to the putter head. These restricted shaft positions can be uncomfortable to a golfer. Secondly, a face balanced putter provides its balanced feature only during the portion of the stroke when the putter head is traveling forward and upward. During the backstroke of a pendulum puffing stroke the face is pointing toward the ground. This situation produces an unbalanced condition and torques due to the force of gravity will result. The outcome is a twisting force imparted to the putter head that can change the intended orientation of the putter face.
Another prior putter, U.S. Pat. No. 5,078,398, states that a shaft axis passing through the center of gravity and strike point of a putter head will impart minimal angular acceleration to the putter head during impact with a golf ball. The above patent also describes a putter shaft axis that passes through the center of gravity of the putter head and the center of gravity of the entire putter. This feature eliminates any unwanted static forces thereby providing "an infinitely balanced" putter. There are several disadvantages associated with this type of balancing scheme. First, this design results in a golfers hands being approximately six inches behind the putter face when addressing a ball. This address position is not commonly accepted; most golfers prefer a putter that provides a hand position in a region directly over the ball. If it is desired to change the lie angle of the shaft by repositioning the hosel stem relative to the club body, the balanced feature of the putter is lost. Secondly, the center of gravity of the entire putter changes once a golfer has gripped a putter. When a golfer is linked with a putter, additional mass is coupled with the entire putter. This additionally linked mass in the form of hands, arms, shoulders, and other moving body parts of a golfer, defines a new and unique system. The new system consists of the pertinent body parts of the golfer and the entire putter. This new system has a center of gravity different from the center of gravity of the entire putter. The center of gravity of the new system is unique to the individual golfer. As a result of this uniqueness, the center of gravity of the system does not necessarily pass through the shaft axis. Therefore, the balanced feature of this putter design is lost. Consequently, it becomes unnecessary to place a constraint on a shaft axis passing through the center of gravity of the entire putter.
Another known putter balancing scheme is the table balanced design. This is where the putter is laid upon a horizontal surface with the club head hanging freely beyond the edge, the putter comes to rest with its striking face aligned vertically. Prior putters, such as U.S. Pat. No. 3,625,517 and U.S. Pat. No. 4,163,554 are examples of table balanced putters. However, the above patents do not incorporate heel and toe weighting for an increased moment of inertia.
The weight distribution of a putter head is an important factor in controlling the amount of twisting force or torque of a putter head during the stroke of the putter. Generally, the majority of the weight in a high moment of inertia putter head is located at the heel and toe regions. This configuration increases the moment of inertia about a point of rotation between the major weight areas. A putter with an increased moment of inertia can reduce the amount of twisting of the putter face during the stroke of the putter. For example, U.S. Pat. No. 4,898,387 cites a putter head with a high moment of inertia. However, there are no built in means of varying the moment of inertia or mass of the club to the personal preference of a golfer. Also, no specific placement of the putter shaft is described to provide a balanced effect. Adjustable weighting schemes have provided built-in custom weighting. Specifically, U.S. Pat. Nos. 4,962,932 and 4,872,684 utilize interchangeable weights at the heel and toe sections of a putter head to satisfy the weighting requirements of an individual golfer. Generally, a golfer will increase the weighting in the heel and toe sections of a putter head with the expectation of increasing the moment of inertia of the putter head. The moment of inertia is defined by two parameters; proportional to the mass of a weight, and proportional to the square of the distance form the mass elements of the weight to a point of rotation. The point of rotation is taken somewhere between the heel and toe sections of the putter head. This definition states that the location of the weight is an important factor. The weights of the above mentioned designs are inserted such that the long axes of the weights are parallel to the face of the putter head. However, this weight alignment can produce unexpected results. The different weights posses different lengths thereby changing the two moment of inertia parameters for a putter head. Consider replacing a lighter (and shorter) for a heavier (and longer) weight in the above mentioned putters. The mass contribution to the moment of inertia will increase. However, the mass distribution of the weight will be shifted towards the point of rotation of the putter head. This shift decreases the distance between the mass elements of the weight and the point of rotation of the putter head. The decreased distance contribution can be larger than the increased mass contribution. Therefore, it is possible to decrease the moment of inertia of a putter head by increasing the weights in the heel and toe of the aforementioned putters. This is an unexpected result. Other adjustable weighted putters have eliminated this unexpected result.
One putter head, U.S. Pat. No. 4,325,553, uses adjustable threaded heel and toe weights such that the long axes of the weights are parallel to the stroke direction of the putter. This scheme produces a constant distance of the mass distribution with respect to a point of rotation regardless of the weights used. Therefore, the moment of inertia of the putter about a designated point changes in an expected manner. However, this putter requires the same mass be inserted in the heel and toe weight receptacles. If a different mass is placed in the heel weight receptacle with respect to the toe weight receptacle, the balanced features of the putter are lost. This constraint on weighting the putter restricts the golfer's individual weighting desires.
The "feel" of a putter produced as a result of impact with a golf ball is an important attribute to a golfer. Prior putters have mass regions deterministically located and may have specific putter head shapes and materials to obtain what a golfer considers a good "feel."One such putter, U.S. Pat. No. 5,131,656, describes a putter with specific mass placement and structural design to promote a solid feel. However, the feel or vibration of this putter is not adjustable. Prior putters have their own vibrational characteristics that are invariant to that putter. No prior an has been witnessed by myself that allows a golfer to adjust in an expected manner the vibrational characteristics of a putter resulting from striking a golf ball.